Device for feeding coal furnaces



Jan. 12, 1937. k v STARK 2,067,583

DEVICE FOR FEEDING COAL FURNACES Filed April 26, 1935 2 Sheets-Sheet l INVEN'I'OR IRGILE STHRK HTTORNEY Jan. 12, 1937., v STARK 2,067,583

- DEVICE FOR FEEDING COAL FURNACES Filed April 26, 1935 2 Sheets-Sheet 2 INVENTOR: \/IRGILE STHFM Patented Jan. 12, 1937 UNITED STATES PATENT OFFICE Application April 26, 1935, Serial No. 18,277 In France May 14, 1934 6 Claims. (01. 19844) This invention relates to improvements for feeding coal furnaces, particularly furnaces burning coal dust.

It particularly concerns furnaces in which the coal, fed from underneath, progresses under the action of a conveyor worm which drives it from a feeding hopper to the base of the furnace.

The combustion of coal of any kind, but particularly that of fine coals, in furnaces of this type, encounters two main difllculties, viz: on the one hand, the necessity of a distribution as uniform as possible of the air necessary for the combustion and, on the other hand, the necessity of counteracting as much as possible clogging caused by clinkers in course of formation. Moreover, it is also extremely important that the coal should be uniformly distributed in the .furnace and to give to the combustion surface a value as high as possible, in order to reduce the losses due to incombustible materials and to obtain, for a given type of furnace, the best efliciency.

The conveyor worm, in the conditions of operation known up to now for this use, does not suitably satisfy the conditions which have just been mentioned. In particular, the distribution of coal in the furnace, especially when it is in the form of coal dust or the like, is far from promoting uniformity of combustion. This comv bustion is slower in the central and upper zones of the furnace than at the periphery of the latter, adjacent to the twyers or blast orifices. The invention relates, in the first place, to a process adapted to improve the feeding of coal furnaces from. underneath, which process essentially consists in imparting to the conveyor worm,

at the same time as its usual movement of rotation, a reciprocating displacement according to its axis, the period of this displacement being in 4 a definite ratio, variable according to circumstances, to the speed of the rotary movement of the conveyor worm.

This process can be carried out by means of various devices all of which, in this application,

v4,5 must be considered as coming within the scope of the present invention.

In order that the process should be clearly.

understood, an improved plant for carrying the same into practice is illustrated, by way of ex- 50 ample and not in a limiting sense, in the accompanying drawings, in which:

Fig. 1 is a vertical section of this plant. Fig. 2 is a top plan view of the same. Fig. 3 is an enlarged side elevation, partly in 65 section, of the left-hand end of Fig. 1.

Fig. 4 is a similar view to Fig. 3 but showing similar parts in section.

In these drawings are to be found the known characteristic features of this type of furnace.

The furnace proper F is, in this example, in the shape of a box having inner walls inwardly curved for receiving the coal. The air for ensuring the combustion is blown into the incandescent mass through twyers or through orifices .o, by means of a fan V. 10

The coal, discharged in a hopper T, is drawn from the base of the latter by a conveyor worm A rotating about its axis :r--.'c, and it is thus brought to the base of the furnace, underneath the mass C in course of combustion. 15

According to the invention, the conveyor worm A, besides its rotary movement known per se, receives a reciprocating movement according to the axis a::r. p

In the example under consideration, the core go a of the conveyor worm carries a member I) provided with rollers g, or their equivalents, which can roll on a cam race d of a fixed member b the latter being, for instance, rigid with the base of the hopper T. A spring R constantly 25 presses the rollers g of the member 1) against the cam race, the shape of this member b corresponding to that of the member 12 In these conditions, the cam race d having a suitable profile, the conveyor worm, at thesame time as 30 it rotates, driven by a motor M, receives an axial reciprocating movement, the relation between both movements of the conveyor worm depending of course on the cam profile d.

The, advantages obtained by means of this im- 5 proved feeding process are the following:

(1) The thrusts exerted by the conveyor worm on the mass of coal C, in front as well as behind, distribute the fuel more uniformly in the furnace. 40

This action can be further improved by providing the front end of the conveyor worm with a head W of special shape, having for instance small inclined faces, the inclination of which can, in each application, be determined by experience or according to the characteristics of the furnace and of the coal to be burnt in the latter.

The presence of these small inclined faces, combined with the reciprocating movement of the conveyor worm, imparts to the coal admitted at the base of the furnace a general movement according to two directions indicated by the arrows 1 -4 that is to say, promoting the supply of coal in the region adjacent to the blast orivfurnace, means for imparting to the screw a fices. In these conditions, the coal has no tendency whatever to accumulate in bulk in the central upper zone.

(2) 1 Owing tothe periodical movement constantly imparted to the mass in course of com- :bustion, the coke whichis formed in front of the blast vtwyers cannot adhere to the latter.

Consequently, the orifice of the twyers not being obstructed; the air, blown in more easily enters the massof coal and ensures a more satisfac- -torycombustion of the latter.

.'(3) The clinkers arising-from the combustion of coal are uniformlydistributed throughout the surface of'the grate, instead of accumulating at certain points.

(4) The constant movement of the mass of 'coal facilitates the propagation of ignition, so that, when starting. the furnace, the combustion spreadsmore rapidly in the mass.

(5) The furnace thus fedcan indifferently receive coals of. different sizes and qualities, the

combustion of said coals alwaystaking place in satisfactory conditions, owing to said-periodical movement.

(6) Finally, this movement tends to prevent wedging of theconveyor-worm, which wedging is in the direction of its axis, a pusher member at the end of said screw disposedin the combus- '.tible mass in the furnace.

2.'A device for feeding coal furnaces, comprising a feeding hopper, a furnace, a conveyor screw between the hopper. and the furnace disposed in a distinctly horizontal manner and emerging under the combustible mass in the said rotative movement about its axis, means for imparting to said screw a longitudinal reciprocatory displacement along its axis efiective during the entire rotation, and a pusher member at the end of the screw disposed in the combustible mass in the furnace.

3. A device for feeding coal furnaces, comprising a fecdinghopper, a furnace, a conveyor screw between the hopper and the furnace emerging under the combustible mass in the latter, means for imparting to the screw a rotative movement about its axis, a fixed member having a cam-race, a movable member rigid with the screw and having rolling members such as rollers engaging said cam race, means for constantly applying the movable member against the fixed member, all for permitting the rotative movement of the screw, and a pusher member at the end of the latter disposed .n the combustible mass in the furnace.

4. A device for feeding coal furnaces, comprising a feeding hopper, a furnace, a conveyor screw between the hopper and the furnace emerging under the combustible mass in the latter, means for imparting to the screw a rotative movement about its axis, a fixed member having a cam-race, a movable member rigid with the screw and having rolling members such as rollers bearing on said cam race, a spring for constantly applying the movable member against the fixed member, means for causing rotation of the movable member while permitting it to slide in the direction of the axis of the screw, and a pusher member at the end of the latter disposed in the combustible mass in the furnace.

5. A device'for feeding coal furnaces, comprising a feeding hopper, a furnace, a conveyor screw between the hopper and the furnace emerging under the combustible mass in the latter, means for imparting to the screw a rotative movement about its axis, a fixed member having a cam-race, a movable member rigid with the screw and having rolling members such as rollers engaging said cam race, a spring for constantly applying the movable member against the fixed member, means for causing rotation of the movable member while permitting it to slide in the direction of the axis of the screw, a pusher member at the end of the latter disposed in the combustible mass in the furnace and inclined faces presented by said member.

6, A feeding device for underfeed stokers comprising a screw conveyor having a casing and a screw therein, and means to impart simultaneous and continuous rotary and reciprocatory movements to said screw, the forward movement of the screw during its reciprocation being of such magnitude as to bodily transport the coal through the casing, said screw projecting forwardly of the casing, and a spindle shaped pusher member on said forward projecting end.

VIRGILE STARK. 

